1. Field of the Invention
The invention relates to system for use in a sound repressive vehicle for giving an interior indication of the presence of remote warning sounds emitted by emergency vehicle sirens, horns and the like, and more particularly, to systems which are responsive to warning sounds reflected from a roadway supporting the vehicle in which the system is installed.
2. Description of the Prior Art
Under modern traffic conditions, and especially in cities with highly congested freeways and streets, wherein high population density inevitably gives rise to frequent emergency events which require summoning of emergency vehicles, including police vehicles, ambulances, fire engines and the like, it is necessary that automobile drivers become aware of the presence of such emergency vehicles as soon as possible. However, modern automobiles are frequently operated with the windows rolled up and with radios operating, so that the vehicle driver often does not hear the sirens of emergency vehicles until the emergency vehicle is very close. At this point, a driver is frequently unable to safely pull over to the side of the road or otherwise move out of the path of the emergency vehicle. Unnecessary delays to emergency vehicles and unnecessary additional accidents are frequently caused by the unawareness of an automobile driver of the presence of an approaching emergency vehicle. The presence of loud external sounds, such as traffic noise produced by the exhausts of diesel trucks and busses and the like further aggravates the problem of early awareness of approaching emergency vehicles. Further, many persons who are legally permitted to drive are nevertheless relatively hard of hearing, and may not hear emergency vehicle sirens sufficiently early to insure complete safety of all parties concerned.
Various attempts have been made to ensure that the driver of a vehicle be alerted to the existence of such external warning sounds. Such systems are generally referred to hereinafter as siren alert systems, even though the warning sounds may be produced by a horn, whistle, warbling device, or the like. Some of the prior siren alert systems have included specialized transmitters located in the emergency vehicle, which transmitters are activated when a siren is activated. However, such systems require specialized receivers located in other vehicles. This state of the art for this type of siren alert system or emergency vehicle alert system is set forth in U.S. Pat. Nos. 3,760,349, 3,233,217, 3,784,970, 4,013,994 and 3,673,560. However, this is an undesirably expensive technique which involves costly transmitters to be installed in all emergency vehicles and expensive receivers to be installed in all vehicles desired to be alerted to the presence of emergency vehicles.
Other siren alert system have incorporated sound transducers such as microphones directionally oriented to detect warning sirens from emergency vehicles to indicate not only the presence, but also the direction from which the emergency vehicle approaches. U.S. Pat. No. 3,626,365 discloses such a system; however, this system is a very complex system, and is therefore unduly expensive. The system described in U.S. Pat. No. 3,626,365 utilizes filter amplifiers which are responsive to signals in the range of approximately 1200 hertz to 8000 hertz. This system is unduly responsive to noises other than those produced by warning sirens, and may cause confusion by indicating the presence of an emergency vehicle when no emergency vehicle is actually near by. U.S. Pat. No. 3,867,719 discloses a siren alert system which provides high selectivity by providing a transducer means tuned to approximately 500 hertz, and operates on the basis of detecting doppler shifts to indicate presence of an amergency vehicle moving rapidly toward the vehicle at which the siren alert system is installed. However, this system is not capable of detecting presence of sirens and the like having no substantial frequency components of approximately 500 hertz. The latter system is complex, and is therefore more costly and less reliable than would be desired.
In different localities of the country, and also in different countries of the world, various sirens or siren-like sound warning devices are common, including single frequency sirens, warbling sirens, air horns, electric horns, and the like. It is highly desirable that a siren alert system be capable of detecting presence of the majority of known types of sirens and sound warning devices, and yet be unresponsive to the numerous other types of noises received by a vehicle, such as traffic noises.
It is therefore an object of the invention to provide a relatively simple siren alert system which detects the presence of warning sounds emitted by a plurality of sirens and sound warning devices operating at a plurality of substantially different frequencies and yet is unresponsive to commonly occurring traffic sounds.
It is another object of the invention to provide a siren alert system which is substantially less complex and costly than siren alert systems of the prior art.